We propose a series of studies with the yeast Saccharomyces cerevisiae and wish to study ribosome structure and function and also the nature of the RNA polymerases in this organism. Antibiotics and mutations to antibiotic resistance will be used and our objectives will be to elucidate the mode of action of antibiotics which act on yeast and other eukaryotes (with special attention to those affecting protein and RNA synthesis). Cell-free systems from yeast and wheat germ will be used for the study of mode of action; in addition, yeast, HeLa cells and rabbit reticulocytes will be used in in vivo studies. Yeast mutants resistant to antibiotics will be isolated, characterized and genetically mapped in order to determine the structural genes for ribosomes, other protein synthesis components and RNA polymerase in yeast. The genetic and biochemical relationship between these mutations and heat-sensitive and cold-sensitive mutants of S. cerevisiae will be used to characterize the latter classes of mutants.